This natural marble cave is one of only five national monuments in Oregon.

This great stone guardian of the forest is a relic from the land's volatile volcanic past.

A rugged lava field dotted with molds of the ancient pines that were growing when the volcano erupted.

Formerly secret, precariously perched boulders.

The decorations were inspired by an unlikely missing treasure.

Once a year, thousands of naked cyclists flood the streets of a Seattle neighborhood.

The longest and widest floating bridge in the world.

An abandoned network of military bunkers and tunnels open for anyone willing to descend into the darkness.

This remarkable collection devoted to the study of fish includes 1 million preserved specimens from all around the world.

Activists are fighting to preserve these unfinished highway ramps as a tribute to the citizen revolt that halted their construction decades ago.

These red and black houses were awarded to the firefighters who saved their city from an enormous blaze.

Legend tells how a Spanish soldier disappeared from this isolated sentry box without a trace.

This bleach-white graveyard overlooking the ocean is accessed through a tunnel.

The largest stone circle in the world has ended up bringing up more questions than it has answered.

The oldest working mechanical clock in the world.

The first archaeological site discovered by aerial photography.

Famously misunderstood wonder of the ancient world

This little replica of Lady Liberty provides a bit of NYC in a Japanese city.

The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

Six ravens are kept captive (but well-fed) at the Tower of London to prevent the fall of the Crown.

A statue marks the exact spot where The Boy Who Never Grows Up made his first literary appearance.

Thanks to modern navigational tools we now know that the true prime meridian runs through a park next door.

This massive collection of British military artifacts includes the heartbreaking personal letters of the men in the trenches of WWI.

Eighty million natural history specimens call this gargantuan museum home.